1. Laser System Status and Plans November 20 th, 2008 R.Febbraro / S. Viret LPC TileCal Operations 1. Diode 4 study 2. Stability preliminary results 3. Next steps

2. 1 R. Febbraro, S. Viret TileCal Operations 1. Diode 4 study 2. Stability status 3. Next steps  What’s the problem with diode 4 ?  Diode 4 not always following the other diodes V. Giangiobbe  Problem was tought to be solved last summer (Diode 4 signal in this case was too low).  We tried to confirm that by taking long runs with large Diode 4 signal.  We were expecting D 4 /D 1,2,3 ratio to be constant along time in this case.

3. 2 R. Febbraro, S. Viret TileCal Operations 1. Diode 4 study 2. Stability status 3. Next steps  First batch of tests:  3 long runs (~1hour) taken by Claudio (Oct, 20 th ): 91964 (Filter 8 / Intensity 23000) 91995 (Filter 6 / Intensity 23000) 92003 (Filter 6 / Intensity 15000) We observed (again…) a problem at the start when the LASER intensity is not stable (runs 91964 & 91998) Problem seems correlated with LASER intensity variation (this one is very small for run 92003) Look at D 4 /D 1,2,3 ratio variation with intensity

4. 3 R. Febbraro, S. Viret TileCal Operations 1. Diode 4 study 2. Stability status 3. Next steps  Second batch of tests:  Short runs taken by Claudio and Renato (Nov, 11,12 th ), all containing Diode 4 information (first time we have that): 94284  303 (Filter 4 / Intensity 15000  27000) 94308  328 (Filter 5 / Intensity 15000  27000)  No filter effect here 94363  375 (Filter 8 / Intensity 15000  27000) Filter 5 runs (Low Gain) Intensity (x10 -3 ) Confirmation of the effect seen by Vincent for Diodes 1,2,3 Effect is nearly absent with Diode 4 !

5. 4 R. Febbraro, S. Viret TileCal Operations 1. Diode 4 study 2. Stability status 3. Next steps  Results: Filter 8 runs (High Gain) Intensity (x10 -3 ) We observe the same behaviour with filters 4 and 8 Intensity (x10 -3 ) Filter 4 runs (Low Gain)

6. 5 R. Febbraro, S. Viret TileCal Operations 1. Diode 4 study 2. Stability status 3. Next steps  Results and conclusions: All the diodes are identical, but the light received by D 4 is not directly proportional to the one received by D 1,2,3 This problem occurs in the LASER box, it could be related to the LASER beam properties, light reflexions in the box,... We will check that during the shutdown.  3in1 card suspected effect is perhaps much smaller than we first tought, but we will also look at it anyway…

7. 6 R. Febbraro, S. Viret TileCal Operations 1. Diode 4 study 2. Stability status 3. Next steps  Why we could still do stability studies with diodes?  Previous results show that having other ‘Diode 4’ covering all the LASER dynamic would be a good idea. We already knew that, but this is a clear confirmation. Transform Diodes 2 and 3 into Diode 4 (using spare PP connectors), should be feasible during the shutdown (not easy tough…).  Until then, Diodes 1,2,3 could still be used for stability tests, as after warm up, the LASER intensity is relatively stable  Diode signal variation might slightly deteriotate the resolution of the calibration, but one could already get interesting results, and develop the calibration software chain.

8. 7 R. Febbraro, S. Viret TileCal Operations 1. Diode 4 study 2. Stability status 3. Next steps  Principle of the study:  We computed the relative ratio variation between two runs (technique described on the web and already presented) but for ALL the calibration runs (8/23000 & 6/23000) taken since this summer (67 runs). 91586 (Low Gain Reference), 91589 (High Gain Reference), 91844 (LG), 91847 (HG), 91848 (HG), 91964 (HG), 91998 (LG), 92423 (LG), 92425 (HG), 93394 (LG), 93396 (HG), 93889 (LG), 93890 (HG), 94371 (HG) Relative variation bet. 2 low gain runs  Results presented here concerns the last month of runs:  The previous macro (which has been ported to python by Chris), has been generalized to loop over all runs. Assuming you have the calib rootuples, it works for all types of runs and for all possible periods.

9. 8 R. Febbraro, S. Viret TileCal Operations 1. Diode 4 study 2. Stability status 3. Next steps  Principle of the study:  On this page you see the runs which were used along with the stability status for each TileCal module.  The macro produces stability plots for all the channels, along with an html page displaying the results: http://atlas-tile-laser.web.cern.ch/atlas-tile-laser/LASERLastMonth.html  A color code tells you if something is wrong.  By clicking on one module you will get detailed information for all the channels (relative ratio variation w.r.t. the reference runs, for all the runs).

10. 9 R. Febbraro, S. Viret TileCal Operations 1. Diode 4 study 2. Stability status 3. Next steps  Module status (LBC 14):  This is what appears when you click on modules.  Once again, color codes shows you bad channels: : no channel info for more than 25% of the runs : bad stability for more than 25% of the runs : bad stability for less than 25% of the runs  : channel OK  In this case things are not too bad…  Open circles show low gain runs evolution, blue points high gain evolution.

11. 10 R. Febbraro, S. Viret TileCal Operations 1. Diode 4 study 2. Stability status 3. Next steps  Module status (EBC 51):  Some modules (in particular in endcaps) are a bit stranger.  This is preliminary work, but the global view makes those things much easier to spot.

12. 11 R. Febbraro, S. Viret TileCal Operations 1. Diode 4 study 2. Stability status 3. Next steps  Where are we now ?  Diode 4 studies have shown that the light sent to the Coimbra box is not directly proportional to the light sent to the monitoring system.  This has to be understood, and if possible solved, during the shutdown.  We should enhance the role (and number) of Diode 4. A temporary solution, based on the actual system, could be setup during shutdown.  Preliminary stability results have been presented, they are available on the web. They show that a very large majority of channels are stable within 2% (even 1% for most of them). This still has to be correlated with other calibration (Cs, CIS, and other LASER method), and could be improved using more events (we use only 3000 for the moment).